In 1949, E. P. Hume wrote an article in the journal Economic
Botany extolling the horticultural virtues of a by-product of the
coconut husk fiber processing industry. Coir is the name given to
the fibrous material that constitutes the thick mesocarp (middle
layer) of the coconut fruit (Cocos nucifera). The long
fibers of coir are extracted from the coconut husk and utilized
in the manufacture of brushes, automobile seat and mattress
stuffing, drainage pipe filters, twine and other products.
Traditionally, the short fibers (2mm or less) and dust
("pith") left behind have accumulated as a waste
product for which no industrial use had been discovered. Hume
write of the excellent growth obtained with various plants when
this coir dust or, as he called it, "cocopeat," was
used as the growing medium (this word has now been registered as
a trademark by one manufacturer of the material).

Hume was a prophet before his time. It is only in the last 10
years that his words of wisdom have percolated through the often
conservative ways of international horticulture. In the 1970's
and 80's, initial tests in Australia and Europe indicated that
coir dust could function remarkably well as a substitute for
various peat products in soilless container media for plant
growth. Several Dutch companies have in fact been using coconut
coir dust in production media since the 1980's, and the Royal
Botanic Gardens at Kew is currently shifting most of its plant
production into coir dust-based media. Sri Lanka (where over 2.5
billion coconut fruits are processed each year) has become the
leading processor of what had previously been considered a waste
product into a form suitable for horticultural use. While other
sources may be available, companies in Sri Lanka have invested
heavily in an infrastructure that guarantees consistency and
quality of the product. Problems that can occur with coir dust
where attention to quality control is not a priority include
contamination with animal manures (with the attendant possibility
of salmonella) and excess salinity. The former can be a problem
in India, where cows often range free. The latter can occur
anywhere where "green" coconuts are harvested for coir
extraction. Unripe nuts are usually soaked in brine to make the
fiber easier to extract, while fresh water is used with fully
ripe coconuts.

Coir dust accumulates in large piles or "dumps"
outside of the mills which process the husks for extraction of
the industrially valuable long fibers. The high lignin and
cellulose content of the pith prevents the piles from breaking
down further. Some of the piles in Sri Lanka are reportedly a
century old! It is this same characteristic that prevents
oxidation and resultant shrinkage of coir dust when it is used as
a growing medium.

As a product of wetland ecosystems, both sphagnum and sedge
peat can't really be considered renewable resources at the level
at which they are harvested from bogs and swamps to satisfy
horticultural demand, despite claims made to the contrary by some
industry representatives. Sedge peat (called "Florida
peat" in that state), the less expensive of the two peats,
is notorious for inconsistency in pH and quality. Sedge peat also
has a tendency to breakdown quickly and sometimes loses volume
after wetting. The superior (and much more expensive) sphagnum
peat has shown wide swings in both price and availability in the
last decade. Consequently, a high quality peat alternative that
is consistently available and also satisfies heightened
environmental concerns would be a "natural" in the
marketplace. But can coir dust grow plants comparable in quality
to sedge and sphagnum peat?

Physical
& Chemical Characteristics

Coir dust is very similar to peat in appearance. It is light
to dark brown in color and consists primarily of particles in the
size range 0.2-2.0 mm (75-90%). Unlike sphagnum peat, there are
no sticks or other extraneous matter.

Independent analyses of coir dust were performed in May and
June 1991 at Auburn University, University of Arkansas, and
A&L Analytical Laboratories (Memphis, TN). These results are
summarized in Tables 1 and 2, and one manufacturer's technical data is
also presented.

G. C. Cresswell (1992) looked at coir dust in comparison to
sedge and sphagnum peat products and concluded that it has
superior structural stability, water absorption ability and
drainage, and cation exchange capacity compared to either
sphagnum peat or sedge peat.

Coir dust tends to be high in both sodium and potassium (Table 2; Handreck, 1993) compared to the
other peats, but Na is leached readily from the material under
irrigation (Handreck, 1993). The high levels of potassium (Table 2) present in coir dust are interesting
to note, and may actually prove more a benefit than any detriment
to plant growth. Coir dust from sources other than Sri Lanka have
also reportedly contained chlorides at levels toxic to many
plants, thus it is very important that salinity in the raw
material be monitored before processing into a horticultural
amendment. It is evident, that chemical properties of this
material can vary widely from source to source (Evans et al.
1996).

The higher pH of coir dust may allow less lime to be added to
a coir dust-based medium, though adding dolomite to container
soils is more important for Ca and Mg nutrition than for
elevating pH. Cresswell did find that a small amount of nitrogen
drawdown (N kept from availability to plants during decomposition
of organic amendments low in nitrogen) occurred with coir dust,
but typical production fertilization practices would likely
compensate for the small amount of resulting N loss. At present,
it is unclear how else fertilization regimes may need to be
adjusted, if at all, in media composed chiefly of coir dust.

Performance
of Coir dust as a Plant Growth Medium

To date, few well designed tests have appeared assessing the
performance of coir dust as a plant growth medium. The few
technical reports, and the much larger anecdotal literature, are
encouraging.

Cresswell (1992) compared coir dust to both sphagnum and sedge
peat as a growing medium for broccoli, tomato and lettuce
seedlings. He found earlier germination and greater size and
uniformity of seedlings germinated and grown in coir dust.
Handreck (1993) tested growth of Petunia x hybrida
'Celebrity Salmon' in 5.6:1 (v:v) mixes of either Malaysian coir
dust, Sri Lankan coir dust, or a sphagnum from Sakhlin, Russia
and silica sand. He observed equal growth when all three mixes
were adjusted to pH 6 and total plant nutrients were supplied,
but varying performance with changes in nutrient regime. He
concluded that plants in coir dust-based media require more Ca,
S, Cu and Fe, but less K, than those grown in peat. He also
observed greater immobilization of soluble nitrogen with coir
dust than peat, an observation confirmed by Cresswell (1992).

Trials at Whittle College in England with several woody
ornamentals in various coir dust/bark blends indicated that coir
dust performance was comparable to sphagnum peat. Unpublished
technical reports from other institutions in England have
indicated similar results with a wide range of greenhouse crops.

I tested the efficacy of coir dust as a peat substitute in replicated trials at the University of
Florida Fort Lauderdale Research Center (Meerow, 1994, 1995).
An ixora, an anthurium, majesty palm, and pentas were grown in
container media that differed only in the peat fraction (40%).
One mix utilized sphagnum, the second Florida (sedge) peat, and
the third, coir dust. The pentas, ixora and majesty palm all grew
much better in the coir dust mix
than in sedge. Interestingly, the anthurium grew almost as
well in the sedge peat mix as in the coir dust. The pentas,
majesty palm and anthurium grew equally well in the coir dust medium as in the sphagnum
medium. Only the anthurium showed slightly better top growth
in the sphagnum mix, a factor I attributed to nitrogen lock-up by
the coir dust.

The sedge peat-based medium had the greatest percent air space and the
lowest water-holding capacity
of the three media at the initiation of the trials, but at
termination, showed considerable reversal of these parameters.
The coir dust-based medium showed the least change in these
parameters over time. The higher initial air porosity of the
sedge-based medium may have been conducive to better initial root
growth of the anthurium, as this plant is epiphytic in nature. No
evidence of Cl or Na toxicity was observed on the plants in this
study grown in the coir dust-based medium, and conductivity measurements indicated
low levels of total dissolved salts.

More informally, I've noticed that seeds sown in a 1:1 (v:v)
mix of coir dust and perlite seem to develop larger root systems
than those germinated in 1:1 sphagnum and perlite. The material
hold up very well under mist, and seems to support less algae
growth than sphagnum. I've been further impressed by the ease
with which coir dust re-wets after it has been thoroughly
dehydrated. I found it takes about 3 hours to "fluff
out" 20 bricks of 9:1 compressed coir dust. Claims have been
made that coir dust is also slightly antibiotic, and thus may
inhibit root pathogens, but this is, to my knowledge,
undocumented.

Availability
of Coir dust

Sri Lankan coir dust is available in bulk from several sources
in the United States and Canada at this time. Lignocell Co. (P.O.
Box 7921, The Woodlands, TX 77387) processes the pith into highly
compressed bricks (9:1; the company may now have switched to a
lower compression ratio) approximately 7.9" X 3.9" x
1.9" in size, each weighing approximately 1.5 lbs. For
commercial growers, the bricks are packed into shrink-wrapped
pallets of 2050 bricks (for retail sale, shrink-wrapped 12-brick
packages weighing 17 lbs. and equipped with handle are
available). A bulk pallet of 2050 blocks measures 7.3' tall x
3.5' wide x 3.8' long, weighs 3000 lbs and will supposedly yield
as much material when re-wet as 128 4-cu. ft. bales of peat moss,
but takes up a fraction of the storage space. Twelve bricks
"fluff out" when re-wet into about 4 cu. ft. of
ready-to-use material. Approximately 2 gallons of water is
required per brick. Similar products are available from GrowCoir,
INC., P. O. Box 154516, Waco, TX 76715, (817) 822-1577; Florikan,
1523 Edger Place, Sarasota, FL 34240, (800) 552-8666; Tierra
Associates, 801 Portola Dr. 202, San Fransisco, CA 94127, (415)
566-4092; and Green Soils, LTD, Canada, (416) 494-9810, (905)
949-4679. Applied Environmental Technologies (2017 Country Ridge
Place, Birmingham, AL 35243) sells a 5:1 compressed bale of coir
dust approximately 27.5" x 14.2" x 5.5." Their
bale requires about 15 gallons of water for rehydration and will
yield about 5 cubic feet of material.

Scotts, Inc. has begun to offer commercial horticultural media
containing coir dust. Local soil mix companies in Florida have
been reluctant to offer coir dust until it can be processed
exactly as they do sphagnum peat. I've found that local companies
charge a premium to rehydrate the bales of coir dust and
incorporate the material into a custom medium.

Compared to Asia, there is little coir production in tropical
America, and, consequently, low supplies of coir dust. Growing
acceptance of the material in the horticultural marketplace is
likely to change this, however, and we may see start-up companies
in our own hemisphere attempting to compete with Sri Lanka and
the Philippines in the future.

The following qualities of coir dust recommend its use as a
peat substitute: 1) high water holding capacity equal or superior
to sphagnum peat, 2) excellent drainage, equal to or better than
sphagnum peat, 3) absence of weeds and pathogens, 4) greater
physical resiliency (withstands compression of baling better)
than sphagnum peat, 5) renewable resource; no ecological
drawbacks to its use, 6) decomposes more slowly than sedge or
sphagnum peat, 7) acceptable pH, cation exchange capacity and
electrical conductivity, and 8) easier wetability than peat.

Coir dust may well be a product whose time has come. The key
issues in developing widespread use of this material in American
horticulture will be price (currently equal to sphagnum peat) and
insuring consistent quality of the coir dusts that enter the
marketplace (Evans et al. 1996).